1. Field of the Invention
The present invention relates to a support structure for a carriage carrying thereon voice coils for drive in such a manner that the voice coils are linearly movable in parallel with a reference plane. More particularly, it relates to a support structure for a carriage which is linearly movable in a radial direction of a disk to form a linear access mechanism.
2. Description of the Prior Art
A carriage which is linearly movable in parallel with a reference plane has been often used in, for example, a linear access mechanism of a magnetic disk device. The linear access mechanism of the magnetic disk device needs a positioning performance having an extremely small positional error. This is inevitable in dense recording/reproducing demands. To improve the performance of the device, there have been various carriage support structures. In the linear carriage support structures, a carriage supporting guide arms having magnetic heads at their distal ends is supported at its underside, so that a pitching will be caused due to a rocking upon the drive or stop or the turbulence in a travel of the carriage, and an error will be generated in the track direction. To improve a dynamic property against such an external turbulence or during the drive, both sides of the carriage are supported so as to suppress deviation of the carriage from the linear motion with rigidity of bearings which supports the carriage, as shown in, for example, U.S. Pat. No. 4,415,941. In such a structure, however, since six support units of the support means are arranged with three of them above the centerline of the carriage and the other below the centerline thereof, the carriage is resiliently deformed and the guide arms are vibrated in directions outside a predetermined plane so that the heads are displaced from the linear motion, resulting in the error generation in reproducing (reading) and recording (writing). In order to cope with this problem, there has been proposed a support structure for a carriage, in which eight support units are used in a support means with half the support units being located on each side of the front and rear sides of the carriage, thereby suppressing the generation of error against the external factor or the like. However, although this support structure is intended to improve the dynamic property to enhance the positioning performance, another problem of reading and describing errors caused by thermal deformation due to heat generation of a voice coil motor for linearly moving the carriage must be solved simultaneously with the improvement of the performance. If such a problem of thermal deformation would not be solved, the carriage would be inclined due to the thermal deformation so that errors in the disc radial direction, i.e., tracking direction would be generated between a servo head for reading out the positional informations and a data head for writing the data. Now, assume that, in the magnetic disk device, the access direction be expressed by an x-axis, a y-axis be set in a plane parallel to the disk, and a z-axis be determined so as to be perpendicular to that plane. In general, a carriage or a fixing portion to which a support member for the carriage is fixed is made of aluminum in order to make the structure light in weight and to improve the machining property. On the other hand, the support member is made of ferric material having a good anti-sliding property. In such a case that a thermal expansion coefficient of the support member is smaller than that of the other member, when the temperature is elevated, a gap or clearance is liable to be created between the support member and the carriage and to be filled with the support member so that the carriage is inclined around the y-axis. When the carriage is inclined around the y-axis, the position of the servo head is displaced as described before, resulting in the generation of positional errors in reading and writing.
Therefore, it is necessary to provide the support structure for the carriage, in which the thermal deformation does not cause the errors in reading and writing.